Chapter 8.2 – Ionic and Covalent Bond

In-text Questions

Question 8.2.1

What is a chemical bond? 

Answer

A chemical bond is a force of attraction that holds two or more atoms together in a molecule or a compound.

Question 8.2.2

On which factor formation of chemical bonds depends?

Answer

The formation of chemical bonds depends on the valence electrons of the atoms involved, their electronegativity, and their ability to gain or lose electrons.

Question 8.2.3

Name the scientists who proposed the electronic theory of chemical bonding?

Answer

The scientists who proposed the electronic theory of chemical bonding are Gilbert Newton Lewis and Irving Langmuir.

Question 8.2.4

Why melting points of ionic compounds are high?

Answer

Melting points of ionic compounds are high because of the strong electrostatic forces of attraction between the oppositely charged ions in their crystal lattice structure.

Question 8.2.5

Why do ionic compounds dissolve in water?

Answer

Ionic compounds dissolve in water because water is a polar solvent that can break the ionic bond by surrounding each ion with an opposite charge, thus allowing them to be carried away in solution.

Question 8.2.6

Name the scientists who discovered noble gases.

Answer

The noble gases were discovered by Sir William Ramsay and Lord Rayleigh.

Question 8.2.7

Write symbols of some noble gases.

Answer

The symbols of some noble gases are He (helium), Ne (neon), Ar (argon), Kr (krypton), Xe (xenon), and Rn (radon).

Question 8.2.8

Write the proposal of Kossel for ionic bond formation. 

Answer

Kossel proposed that ionic bond formation involves the transfer of electrons from one atom to another to achieve a stable octet configuration in the valence shell of both atoms.

Question 8.2.9

What is the octet rule? 

Answer

Octet rule states that atoms tend to combine in such a way that they have 8 electrons in their valence shell, which is considered a stable configuration.

Question 8.2.10

What is the crystal shape of NaCI? 

Answer

The crystal shape of NaCl is a face-centred cubic lattice structure.

Question 8.2.11

Why ionic compounds do not conduct electricity solid state? 

Answer

Ionic compounds do not conduct electricity in a solid state because the ions are not free to move and carry the electrical charge.

Question 8.2.12

State a limitation of the octet rule. 

Answer

One limitation of the octet rule is that it doesn’t apply to elements beyond the second period of the periodic table and can’t explain their bonding behavior well.

Question 8.2.13

Why covalent compounds are low melting?

Answer

Covalent compounds are low melting because they have weak intermolecular forces of attraction between the molecules, which require less energy to break.

Question 8.2.14

Which elements form covalent molecules?

Answer

Non-metallic elements form covalent molecules.

Question 8.2.15

Will sodium and chlorine form a covalent bond?

Answer

No. Because the electronegativity difference between these two elements is very high they will always form an electrovalent bond.

Question 8.2.16

In HF molecule which element has fulfilled octet.

Answer

In HF molecule, fluorine (F) has fulfilled octet.

Question 8.2.17

Name the types of double bonds. 

Answer

The types of double bonds are sigma (σ) and pi (π) bonds.

Question 8.2.18

Are the two O atoms in the O₂ molecule bonded by two covalent bonds or one covalent bond?

Answer

The two O-atoms in the O₂ molecule are bonded by two covalent bonds.

Multiple Choice Questions (MCQ)

Question 1

Chemical bond is

1. electrical force
2. gravitational force 
3. only magnetic force
4. None of these

Answer

Chemical bond is an electrical force that holds two or more atoms together in a molecule.

Question 2

Covalent compounds are generally

1. soft
2. hard
3. soluble in water
4. conduct electricity

Answer

(a) Soft

Explanation :

Covalent compounds are generally soft, have low melting and boiling points, are not soluble in water, and do not conduct electricity.

Question 3

The percentage of noble gas present in the air is

1. 5%
2. 0.01%
3. 1%
4. 21%

Answer

(c) 1%

Explanation : 

The percentage of noble gas present in air is 1%.

Question 4

In an electrovalent bond there is an electron

1. between two atoms
2. between two atoms or molecules
3. between two molecules
4. None of these

Answer

(d) None of these

Explanation:

In an electrovalent bond, there is an electron transfer between two atoms or molecules.

Question 5

The shape of the NaCl crystal is

1. tetrahedral
2. octahedral
3. hexagonal
4. icosahedral

Answer

The shape of the NaCl crystal is octahedral.

Very Short Answer Type Questions (VSA)

1. Ionic compounds are soluble in ____ solvents. (polar / non-polar) 
2. Density of nitrogen collected from air is ____ g/L at STP. (1.2572 / 1.2506) 
3. Theory of ionic bond formation proposed by ____ (Kossel / Lewis) 
4. In BF₃, Octet of valence shell is fulfilled ____. (B / F)

Answer

Indicate which statement is true and which one is false: 

1. In a crystalline state, NaCl conducts electricity. 
2. Ni²⁺ ion has 8 electrons in its valence shell. 
3. Generally melting and boiling points of ionic compounds are high. 
4. No covalent compounds conduct electricity in any state.

Answer the following questions

Question 1

Between N₂ and CH₄ which molecule has multiple covalent bonds? 

Answer

N₂ has a triple covalent bond, while CH₄ has only single covalent bonds.

Question 2

Write the electron dot and dash structure of CO₂ molecule. 

Answer

In the electron dot and dash structure of CO2, the carbon atom is double-bonded to each of the two oxygen atoms, and each oxygen atom has two lone pairs of electrons.

Question 3

Name the scientists who proposed the electronic theory of valency. 

Answer

Gilbert Newton Lewis and Walter Kossel proposed the electronic theory of valency.

Question 4

Between NaCl and CH₄ which dissolves in benzene. 

Answer

Between NaCl and CH₄, CH₄ is the substance that can dissolve in benzene, while NaCl is not soluble in benzene due to its ionic nature and the nonpolar nature of benzene.

Question 5

Between Cl atom and Cl^– ion, which one is stable? 

Answer

Cl^– ion is more stable than Cl atom.

Question 6

Name the scientists who discovered Kr and Xe. 

Answer

Sir William Ramsay and Morris Travers discovered Kr and Xe.

Question 7

Between LiCl and HCl which is an ionic compound?

Answer

LiCl is an ionic compound, while HCl is a covalent compound.

Short answer type questions

Question 1

How HF molecule is formed from H- and F- atoms? Explain with electron dot structure. 

Answer

HF molecule is formed from H and F atoms by the sharing of electrons between the two atoms. In the electron dot structure of HF, the valence shell of H has one electron while the valence shell of F has seven electrons. One electron from the valence shell of H is shared with seven electrons of the valence shell of F to form a covalent bond. The shared electrons are shown by a dash between H and F.

Question 2

Explain the formation of N₂ molecules from N- atoms. 

Answer

N₂ molecule is formed from N atoms by the sharing of electrons between the two atoms. Each N atom has five valence electrons. Two N atoms share three electrons each to form a triple covalent bond. The electron dot structure of N₂ shows three pairs of shared electrons between the two N atoms.

Question 3

How many covalent bonds are there in C₂H₂? Show by dash structure. 

Answer

There are three covalent bonds in C₂H₂. The electron dot structure of C₂H₂ shows that each carbon atom shares a triple bond with the other carbon atom, and a single bond with each of the two hydrogen atoms.

Dash structure:  H−C ≡ C−H

Question 4

Mention the limitation of octet rule in covalent bond formation. 

Answer

Some elements such as H, He, Li, and Be can form stable molecules with less than 8 electrons in their valence shell. On the other hand, some elements such as P, S, Cl, and Br can form stable molecules with more than 8 electrons in their valence shell.

Question 5

Why covalent compound HBr conduct electricity in an aqueous solution? 

Answer

The covalent compound HBr conducts electricity in an aqueous solution because it undergoes dissociation into ions in the presence of water. The hydrogen ion (H⁺) and bromide ion (Br^–) formed during dissociation are responsible for the conduction of electricity.

Question 6

What type of bond present in (i) NaH (ii) HCl (iii) CCl₄ (iv) K₂O

Answer

1. NaH has an ionic bond between Na⁺ and H^– ions.
2. HCI has a polar covalent bond due to the unequal sharing of electrons between the hydrogen and chlorine atoms.
3. CCl₄ has a covalent bond due to the sharing of electrons between the carbon and chlorine atoms.
4. K₂O has an ionic bond between K⁺ and O^2- ions.

Long Answer type questions

Question 1

Describe briefly the discovery of noble gases. 

Answer

Several scientists discovered Noble gases in the late 19th century, including Henry Cavendish, John William Strutt (Lord Rayleigh), and William Ramsay. In 1894, Ramsay and Lord Rayleigh discovered argon, the first noble gas, by isolating it from the air. They later discovered helium, neon, krypton, and xenon by using a similar method of fractional distillation of liquid air. The name “noble gases” was given to this group of elements because they were thought to be chemically inert and did not easily react with other elements.

Question 2

Write the limitations of the octet rule in chemical bond formation. 

Answer

The limitations of the octet rule in chemical bond formation are:

1. The octet rule is not applicable to elements that have more or less than eight electrons in their valence shell, such as boron and phosphorus.
2. The octet rule does not explain the bonding in molecules that involve atoms with odd numbers of electrons, such as NO and NO₂.
3. The octet rule assumes that all atoms in a molecule have the same electronegativity, which is not always true in reality.
4. The octet rule does not explain the phenomenon of resonance, where multiple Lewis structures can represent a single molecule.

Question 3

Write the properties of ionic compounds. 

Answer

Question 4

Write the properties of covalent compounds, and how these properties differ from that of NaCl. 

Answer

The properties of covalent compounds are:

1. Low melting and boiling points: Covalent compounds have weak intermolecular forces between molecules, so they have lower melting and boiling points than ionic compounds.
2. Insolubility in water: Covalent compounds are generally insoluble in water as they do not dissociate into ions and therefore cannot form hydrogen bonds with water molecules.
3. Non-conductivity: Covalent compounds do not conduct electricity in any state because they do not have free-charged particles.
4. Softness: Covalent compounds are generally soft and have a low hardness because their molecules are held together by weak intermolecular forces.

Comparison with NaCl (Ionic Compound):

1. Melting and Boiling Points: NaCl (ionic) has high melting and boiling points, while covalent compounds have lower melting and boiling points.
2. Solubility in Water: NaCl is highly soluble in water, whereas many covalent compounds are either poorly soluble or insoluble.
3. Conductivity: NaCl conducts electricity when dissolved in water or molten, but covalent compounds do not conduct electricity in either state.
4. Physical States: NaCl is a solid at room temperature, while covalent compounds can exist as solids, liquids, or gases at room temperature.

Question 5

What do you mean by chemical bond?

Answer

A chemical bond is an attractive force that holds atoms or ions together in a molecule or compound. It arises from the interaction between the electrons in the outermost shell (valence shell) of the atoms. Chemical bonds can be classified as ionic, covalent and coordinate bonds.

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